Magnetic sound recording and monitor system



Se t. 3, 1940. H.,s. HELLER MAGNETIC SOUND RECORDING AND MONITOR SYSTEM Filed oct. 25, 1937 Anm.. H7

nvenor. Herma/n ,5. Heller.

orney.

Patented Sept. 3, 1940 UNITED STATES MAGNETIC SOUND RECORDING AND MONITOR SYSTEM Herman S. Heller, West Los Angeles, Calif.

Application October 25, 1937, Serial No. 170,986

This invention relates generally to magneticrecording and reproduction of sound, and deals particularly with a high fidelity system for the magnetic recording and reproduction Vof sound throughout an extended frequency range.

A limitation in the magnetic recordation and reproduction of sound has been the comparatively limited frequency range which can be elciently recorded and reproduced by the usual translating magnets. If the magnets are provided with such impedance characteristics as to reproduce effectively and eiiciently for a median frequency level, there is substantial attenuation in both the high and low frequency regions.

l5 It is accordingly one primary object of the present invention to provide a sound recording and reproduction system of the magnetic type capable of recording and reproducing a substantially extended range of audible frequencies.

A further object of the invention is to provide a monitor system by which the sound may be audibly reproduced from the record as recorded thereon, so that the operator may adjust the recording system guided by the quality of such reproduction.

In accordance with the present invention, the magnetic recording element is in the form of a hat tape, and a multiplicity of translating magnets are employed, spaced transversely of said V 3g tape, so as to produce a multiplicity of separate,

adjacent recordings on the tape. The several translating magnets are tuned to different frequency ranges, and together produce a multiplicity of recordings adequately covering the full audible' frequency range. The magnetic tape is thus impressed with a multiplicity of records, each corresponding to a designated region of the audible frequency range, and the set of recordings taken together covering` substantially the o entire audible range without serious attenuation at any frequency level within the range covered. A feature of the invention is the provision of a corresponding set of monitoring translation mag. nets and suitable output circuits leading to a loud speaker, adapted to reproduce the rocords as they are made, so that, if desirable, the relative amplitudes of the recording currents produced within the recording magnets may be adjusted with relation to one another.

The invention will be best understood by referring now to the following detailed description of a present, simple illustrative form of the invention, reference for thispurpose being had to the accompanying'drawing which is a diagrammatic view illustrative of the invention.

The travelling magnetic tape is indicated in the drawing at M. This tape may be typically .125" in width and .002" in thickness, though these indicated dimensions are not to be taken 1n any way as limitative 'onVI the invention. 6 Tape M, travelling in the direction of the arrows, passes first between two pairs of polarizing or erasing magnets l0 and Il, preferably offset a short distance in a direction longitudinally of the tape. These magnets comprise windings i2 and 10 pole pieces i3, the latter extending transversely of the tape and being of substantially the width of the tape. In the present illustrative form of the invention, the tips of these pole pieces bear lightly on thel surface of the tape. It is desir- Il able that the pole pieces be yieldingly pressed, with a comparatively light pressure, against opposite surfaces of the tape, and this may be done with spring means such as shown in Patent No. 2,003,968 to Hickman et al., or as shown in my 20 copending application entitled Sound head for magnetic recording machines, filed October 25, 1937, Serial No. 170,985. Magnets l0 and il are here shown as series connected in a circuit I5 including polarizing battery l1 and switch i8. 25 It will be understood that the function of polarizing magnets i0 and Il is to polarize tape M to saturation, thus erasing or obliterating the previous recording on the tape. The reason for using two pairs of such magnets is simply to assure 30 full and effective polarization; in many instances one such pair will of course be adequate. It will also be understood, however, that the purpose of the magnets i0 and I i is to erase or obliterate any Vpast recording on the tape, and that 35 any well known or suitable method of energizing the erasing magnets may be employed, as desired, whether direct current, as shown, or high frequency alternating current, which leaves the tape totally demagnetized, both of which metho ods are well understood in the art.

After passing between erasing magnets i0 and Il, the tape passes next between a multiplicity of translating magnets 20, 2i and 22, spaced laterally of the tape, so as to record on 45 adjacent recording lanes a, b and c as indicated in the drawing. Each of these translating magnets comprises a winding 2| and a pole piece 25. For a magnetic tape of the dimensions previously given, pole pieces 25 may be, for example, 50 of a thickness dimension of .015 and of a width of approximately .125", the inner ends or tips of the pole pieces being tapered and beveled to an edge preferably not over approximately .003" in thickness, and of a dimension at right angles 55 to the tape approximately, or slightly less than.,

one-third of the width of the tape (assuming three recording lanes). The tips of the pole pieces may be formed initially| with a comparatively sharp, chisel-like edge, but by reason of wear on the tape are soon blunted somewhat and operate satisfactorily, with comparatively slow speed of tape, at a thickness dimension of from .001" to .003". Reference is here made to a copending application of myself and Leo G. Butler, entitled Method of and appa.- ratus for magnetically recording sound, Ser. No. 170,988, filed October 25, 1937, in which pole pieces of the kind here referred to are disclosed and claimed. Pole pieces 25 also bear lightly on the surfaces of the tape. preferably being pressed inwardly by spring devices, not illustrated, as mentioned in connection with polarizing pole pieces I3.

The pole pieces are disposed in planes at right angles to the direction of travel of the tape, and with thetips of each pair preferably directly opposite one another, the pole tips of successive pairs of pole pieces extending transversely across, or covering, adjacent longitudinally extending lanes a, b and c of the tape.

'I'he windings of magnets 20, which are series connected, are connected to conductors 30 and 3|. the latter going to a variable resistor 32, the other side of which is connected by` wire 33 to a lead 34. Conductor 30 is connected to a lead 35. A condenser 36 is connected in shunt across magnets 20. Similarly, magnets 2|, also series connected, are connected to conductors 40 and 4|, the former vbeing directly connected to lead 35, and the latter being connected to variable resistor 42, the other side of which is connected by wire 43 to lead 34, while series connected magnets 22 are connected to conductors 60 and 5|, conductor 50 being connected to lead 35, and conductor 5| being connected to resistor 52, the

other side of which is connected by wire 53 to lead 34. Condensers 41 and 51 are connected across pairs of magnets 2| and 22, respectively.

Lead 34 is connected to contacts 60 and 6| of a control switch S, while lead 35 is connected to contacts 62 and 63 of said switch,

A microphone, indicated at 66, is connected via variable-loss T pad 68to wires 69 and 10 connected to contacts 1| and 12, respectively, of switch S. Pad 68, which is conveniently indicated, is of a well known type, variable for instance by steps of one and one-half db. The complete network of resistances involved in such a pad is well understood in the art and is therefore indicated only conventionally in the figure, it

being suicient to state that pad 68 is variable to control the loss in the microphone circuit by predetermined and preferably equal steps.

When switch S is thrown to record position, a switch arm 13 makes with contact 1|, a switch arm 14 makes with contact 12, a switch arm 15 makes with contact 62, and a switch arm 16 makes with contact 6|.. Switch arm 13, thus connected to microphone lead 10, is connected by lead 13 to one end of the primary Winding 19 of an amplifier input transformer 80, while switch arm 14, connected to the other microphone lead, is connected by lead 8| to an intermediate tap of the primary of input transformer winding 13. The secondary winding of transformer is connected to the input end of an amplifler l5, typically of the vacuum tube type. Output leads 31 and 88 of amplifier 85 are connected to the aforementioned switch arms 15 and 16, respectively, land are thus connected to leads 34 and 36,.

across which the translating magnets are connected in parallel. Microphone 66 is thus connected through switch S and amplifier Il to parallel-connected translating magnets 2l, 2| and 22, so that a speech or music input to the microphone produces a corresponding sound current which, after amplification, flows in said translating magnets.

Each pair of translating magnets is tuned to respond to a given lband of frequencies, the three pairs of magnets covering substantially the audible frequency range. Thus magnets 20 are tuned to the low frequency end of the audible range, magnets 2| to an intermediate frequency band, and magnets 22 to the high frequency end of the audible range. For example, though without intention of limiting the invention, the coils of magnets 20 may be wound to a total inductance of .25 henry, the coils of magnets 2| to a total inductance of .1 henry and the coils of magnets 22 to a total inductance of .022 henry, while condenser 36 connected in parallel with magnets 2l has a capacitance of .25 mf., condenser 41 in parallel with magnets 2| has a capacitance of .1 mf., and condenser 51 in parallel with magnets 22 has a capacitance of .02 mf. With these values of inductance and capacitance, magnets 2l have a peak response of 100 cycles and reproduce from 40 cycles to 850 cycles with no more than a 2 db. loss from the 100 cycle resonance peak; magnets 2| have a peak response of 1,700 cycles and respond from 850 cycles to 4,000 cycles with no more than a 2 db. loss from the 1,700 cycle resonance peak; while magnets 22 have a peak response of 6,500 cycles and respond from 4,000 cycles to 10,000 cycles, also with no more than a 2 db. loss from the resonance peak. The three sets of coils thus adequately cover the full range of audio frequencies that are commonly deemed important in sound recording and reproduction. It will of course be understood that while three sets of tuned magnets are here shown, the advantages of the present invention may be gained to some extent by the use of but two sets of tuned magnets, or even greater uniformity of response and even greater coverage of the audio frequency range may be obtained by using more than three tuned sets of magnets, the present illustrative use of three sets of tuned magnets being simply illustrative of a typical form of the invention.

Sound currents produced at microphone 6l and. amplified at amplifier are acccordingly divided between tuned translating magnets 20, 2| and 22, currents of frequencies from 40 cycles to 850 cycles flowing predominantly in magnets 2l, and therefore being recorded predominantly on recording lane a, currents of frequencies from 850 cycles to 4000 cycles flowing predominantly in magnets 2| and therefore being recorded predominantly on recording lane b, and currents of frequencies from 4000 cycles to 10,000 cycles iloving predominantly in magnets 22 and being recorded predominantly on recording lane c. The total range covered in the typical instance here given is from 50 cycles to approximately 7500 cycles with a 2 db. variation. It is well known that a 2 db. variation is not noticeable to the ear. This total range is much greater than can be covered with a single pair of recording magnets.

The variable pad 43 controls the volume level of recording of the three sets of translating magnets as a group, while variable resistors 32, 42 and 52 control the current strengths flowing in the three sets of magnets with relation to one another, and thus may be employed to vary the volume levels at which the upper and lower frequency ranges are recorded with relation to each 5. other and to the level of the intermediate range.

When switch S is moved in the opposite direction, to reproduce, switch arm 13. makes with contact 83 connected to translating coil lead 35, and a' switch arm |00 makes with contact 60 connected to translating coil lead 34. Switch arms 13 and |00 are connected via variable loss T pad |04 (which may be of the same general type as the aforementioned T pad 68) across the end terminals of primary winding 19 of ampliiier input transformer 80. At the same time, switch arms and 16 make with contacts |05 and |06 connected by leads |01 and |08, respectively, to loud speaker |09. It will be evident that translating coils 20, 2| and 22 are then connected through switch S and amplifier 85 to loud speaker |09, and that if a tape M, having a previous recording thereon, made as previously described, is run between said coils 20, 2| and 22, the recordings on the several lanes of the tape will produce corresponding sound currents in magnets 20, 2| and 22, which will flow in the described circuiting to amplifier 85, and after amplification, will flow to speaker |09 and be reproduced as audible sound. Since each set of tuned translating magnets is now reproducing a recording of a frequency range to which that translating magnet is tuned (the several recordings on the tape having been made by the same magnets now being utilized for reproduction, or 35; by magnets exactly similar thereto), the entire frequency range recorded on the several lanes of the tape is reproduced without loss.

A monitor system is provided, for use during recording, enabling the recording to be reproduced as it' is being made, so that adjustments of the volume levels at which the different frequency bands are recorded on the tape may be adjusted as desired during the recording operation.

For this purpose, three pairs of translating magnets |20, |2| and |22, exactly like magnets 20, 2| and 22, respectively, are provided just beyond translating magnets 20, 2| and 22, so that the tape coming.. from the latter magnets passes 50, immediately between magnets |20, |2| and |22. 'Ihus magnets |20, |2| and |22 comprise windings |24 having the same inductances as the windings of magnets 20, 2| and 22, respectively, and have pole pieces |25 exactly like the pole 55 pieces 25 af magnets 20, 2| and 22. Magnets |20, |2| and |22 are spaced transversely of tape M in a manner exactly similar to magnets 20, 2| and 22, so that magnets |20, |2| and |22 will reproduce the recordings made on lanes a, b and 60.K c, respectively. The distances along the tape be- ""tween magnets andA |20, 2| and |2|, and 22 and |22 are exactly equal to one another. The tip of pole pieces |25 bear lightly on the surfaces of tape M in the same manner as do the tips of 65,; pole pieces 25, being preferably provided with "spring devices, not illustrated, yieldingly urging them toward the tape, as described in connection with pole pieces |3 and 25.

'I'he pairs of magnets |20, |2| and |22 are 70 series-connected, and are connected to leads |21 and |28, |29 and |30, and |3| and |32, respectively. Leads |21, 29 and |3| are connected to a lead going to one input terminal of ampli- Iier |31, and leads |28, |30 and |32 are connected 75 to a lead |36 going to another input terminal Condensers |4|, |42 and |43, of the same ca-` pacitances as condensers 38, 41 and 51, respectively, are connected across pairs of leads |21 and |28, |29 and |30, and |3| and |32, respectively. Magnets |20, 2| and 22 are thus tuned to the same frequency bands as magnets 20, 2| and 22, respectively. It will be evident that the low frequency sound band recorded on tape lane a by means of low frequency recording magnets 20 will be substantially exclusively or predominantly reproduced as sound currents within magnets |20, and that'similarly the middle frequency and high frequency band recordings produced on tape lanes b and c by recording magnets 2| and 22 will be reproduced as corresponding sound currents substantially exclusively predominantly Within magnets |2| and |22, respectively.

Reproducing magnets |20, |2| and |22 are located just beyond recording or translating magnets 20, 2| and 22, so that during recording the different frequency band records produced on the tape by said recording magnets are immediately translated to corresponding sound currents within magnets |20, |2| and |22, which are amplified at |31 and audibly reproduced by speaker |40.

The operator is therefore enabled to listen back to the recording substantially as it is made, and, if desirable, may readjust the variable pad 63, or the variable resistors 32, 42 and 52, guided by the audible reproduction at speaker |40. The recording is thus initially made at the volume level desired, and with the desired balance between the volume levels of the several limited frequency band recordings on the tape. The first record made may therefore be a perfect record, rather than requiring volume modication during a re-recording operation, as in other recording systems.

It will be understood that the system as now described and illustrated is simpy illustrative of rather than restrictive on the broad invention,

and that various changes and rearrangements.

may be made without departing from the spirit and scope of the invention or of the appended claims.

I claim:

1. In a magnetic recording system, the combination of a iiat/magnetizable tape, means guiding said tape for movement along a fixed line of travel, a plurality of pairs of translating electromagnets mounted in operative relation to said tape along said line of travel and positioned in oiiset relation transversely of the tape so as to act on adjacent longitudinally extending lanes of the tape, said pairs of translating electromagnetsl having windings andl individual input circuits tuned to different frequency ranges, individually controllable volume control means in said individual input circuits, sound current input means connected to said circuits, a plurality of pairs of monitoring reproducing electromagnets mounted. in operative relation to saidy tape beyond said rst mentioned electromagnets, said pairs of monitoring electromagnets being positionedin offset relation transversely of the tape, so that individual pairs of said monitoring electromagnets correspond in position transversely of the tape to individual pairs of said translating electromagnets, all transversely corresponding pairs ofv said translating and monitoring magnets being spaced apart longitudinally of the tape by the same distance, said pairs of reproducing magnets having windings and individual output circuits tuned to the same frequency ranges. respectively, as the windings and individual input circuits of said circuits of said corresponding pairs of translating magnets. and sound reproducing means connected for reproduction of sound corresponding to sound currents flowing in said output circuits.

2. In a magnetic recording system, the combination` of a flat magnetizable tape, means guiding said tape for movement along a fixed line of travel. a plurality of pairs of translating electromagnets mounted in operative relation to said tape along said line of travel and positioned in oiset relation transversely of the tape so as to act on adjacent longitudinally extending lanes of the tape, said pairs of translating electromagnets having windings and individual input circuits tuned to different frequency ranges, sound current input means connected to said circuits, a plurality of pairs of monitoring reproducing electromagnets mountedin operative relation to said tape beyond said ilrst mentioned electromagnets, said pairs of monitoring electromagnets being positioned in offset relation transversely of the tape, so that individual pairs of monitoring electromagnets correspond in position transversely of the tape to individual pairs of said translating electromagnets, all transversely corresponding pairs of said translating and monitoring magnets being spaced apart longitudinally of the tape by the same distance, said pairs of reproducing magnets having windings and individual output circuits tuned to the same frequency ranges, respectively, as the windings and individual input circuits of said corresponding pairs of translating magnets, and sound reproducing means connected for reproduction of sound corresponding to sound currents ilowing in said output circuits.

3. In a magnetic'recording system, the combination of a flat magnetizable tape, means guiding said tape for movement along a xedline of travel, a plurality of pairs of translating electromagnets mounted in operative relation to said tape along said line of travel and. positioned.- in offset relation transversely of the tape so as to act on adjacent longitudinally extending lanes of the tapesaid pairs of translating electromagnets having windings and individual input circuits tuned to different frequency ranges, individually controlling volume control means in said individual input circuits, sound current input means connected to said circuits. a variable loss pad controlling the total input current from said sound current input means to said individual input circuits, a plurality of pairs of monitoring reproducing electromagnets mounted in operative relation to said tape beyond said ilrst mentioned electromagnets, said pairs of monitoring electromagnets being positioned in offset relation transversely of the tape, so that individual pairs of said monitoring electromagnets correspond in position transversely of the tape to individual pairs of said translating electromagnets, all transversely corresponding pairs of said translating andmonitoring magnets being spaced apart longitudinally of the tape by the same distance, said pairs of reproducing magnets having windings and individual output circuits tuned to the same frequency ranges, respectively, as the windings and individual input circuits oi said circuits of said corresponding pairs of translating magnets, and sound reproducing means connected for reproduction of sound corresponding to sound currents ilowing in said output circuits.

4. In a magnetic recording system, the oombination o f a iiat magnetizable tape, means guiding said tape for movement along a nxed line oi travel, erasing magnet means positioned inoperative relation to said tape along said line of travel adapted to act on the entire width of the tape. a plurality of pairs of translating electromagnets mounted in operative relation to said tape along said line of travel and positioned beyond said erasing magnet means in the direction of travel of the tape, said pairs of translating magnets being positioned in oiIset relation transversely of the tape so as to act on adjacent longitudinally extending lanes of the tape, said pairs of translating electromagnets having windings and individual input circuits tuned to different frequency ranges, and sound current producing means connected to said circuits. l

5. In a magnetic recording system, the combination of a fiat magnetizable tape, means guiding said tape for movement along a iixed line of travel, a pair of erasing electromagnets positioned on opposite sides of said tape, pole pieces in said electromagnets contacting opposite surfaces of said tape and extending transversely of the tape substantially the full width thereof, a plurality of pairs of translating electromagnets positioned with the members of each pair in end to end opposition and on opposite sides of the tape, pole pieces in said electromagnets contacting limited widths of the tape, and said pairs of electromagnets being so spaced transversely of the tape that the pole pieces of diierent pairs of electromagnets contact and act on adjacent longitudinally extending lanes of the tape, said pairs of translating electromagnets having windings and individual input circuits tunedto different frequency ranges, and sound current producing means connected to said circuits.

6. In a magnetic recording system, the combination of a flat magnetizable tape, means guiding said tape for movement along a iixed line of travel, a plurality of pairs of translating electromagnets mounted in operative relation to said tape along said line of travel, said pairs of translating electromagnets being offset transversely of the tape so as to act on adjacent longitudinally extending lanes of the tape, erasing magnet means positioned in operative relation to said tape along said line of travel and positioned ahead of said translating electromagnets in the direction of travel of the tape, said erasing magnet means being positioned and adapted to act on the width of the tape actedon by all of said pairs of oifset translating electromagnets, said pairs of translating electromagnets having windings and individual input circuits tuned to different frequency ranges, and sound current producing means connected to said circuits.

.HERMAN S. HELLER, 

